Bridge full screen preview background transparency bug

Hello

I have a peculiar interface anomaly occurring in Bridge when I view images full screen by pressing the space bar. Whenever I do this the background and/or image exhibits partial transparency (about 30%) around the very edges of the screen and I can see my desktop showing through. This strip of partial transparency is about 1cm (1/2 inch) wide and bleeds gradually into the background. Strangely the desktop image that shows through appears to be a ghost image of sorts because it remains the same even if I change the desktop. What's more peculiar is that I tried to screen grab the effect so I could share it here but the screen grab does not capture this anomaly. In the screen grab the background looks normal and runs right to the edge of the screen! I have this happening in both Bridge 2019 and 2018. I'm using a 27" 5K iMac running OS High Sierra (10.13.6).

Anybody out there able to shed some light on this please?